Anatomy of the Jejunum and Ileum

00:01 So now let's have a look at the jejunum and the ileum. We spend a lot of the time talking about the duodenum.

00:06 So, the jejunum is the more proximal part of the gut tube when we're talking about the small intestines. And the ileum is much more distal. And they are different. Sometimes it can be quite difficult to pick out that difference when you look at them if you just pick up a random piece of small intestine, but actually they are very different. If you look at the proximal bit of the small intestine and a very distal part of the small intestine, they will characteristically be different. So here we can see the differences in both of those. The jejunum is much more substantial than the ileum. We have a diameter from around 4 cm compared to that of 2 with the ileum. The walls of the jejunum are that much thicker, is that much greater vascular that is going towards this region compared to the ileum. There are many, many circular folds and there are much fewer circular folds when we look at the ileum indicating the difference in its digestive properties. The color of the jejunum is much pinker, if not red, compared to the ileum.

01:06 That's because of the high vasculature. There's much more blood going towards this region. And actually if you look at lymphoid nodules, that's the only thing where there's a reduction in something. In the jejunum, there's fewer lymphoid nodules in this region as opposed to the ileum where there's many, many lymphoid nodules. Surrounding the jejunum, we find there's much less fats within the mesentery but within the ileum there are much more fats located within the mesentery. The mesentery is something that we'll come to later on. It's a peritoneal structure that helps to hold and suspend the ileum within the abdominal cavity. As I've mentioned before, there are many more blood vessels within the mesentery that give rise to the much redder coloration of the jejunum compared to the pinker or less red coloration of the ileum. And that's due to the fact there's more or less blood going towards that region. If we have a look at the jejunum and the ileum and the relations of the structures within the abdomen, you could see the jejunum and ileum are smocked banged really within the central portion of the abdomen. Flanking it on its right hand side, we have the ascending colon. Here, you could see the vermiform appendix attached to the cecum and then you have the ascending colon going up towards the liver. Going from the right hand side to the left hand side of the abdomen, we move from the ascending colon to the descending colon by the transverse colon. And here we can see the descending colon passing all the way down into the pelvis. The descending colon then gives rise to what's known as the sigmoid colon and the sigmoid colon is ___ aspect of the colon that passes down towards the pelvis.

02:45 It passes posterior to the urinary bladder, which we can see there. So the jejunum and ileum are these coils of mass small intestine that are situated very much within the central aspect of the abdomen.

02:58 Covering over the jejunum and the ileum is this structure mentioned before which is the greater omentum.

03:04 And this is an apron fatty tissue productive of peritoneum as we'll talk about in a later topic, but it covers very much the whole anterior surface of the small intestine.